1. Robert S. Laramee r.s.laramee@swansea.ac.uk 1 http://cs.swan.ac.uk/~csbob/ 1 Flow Like You've Never Seen It Robert S. Laramee Visual and Interactive Computing Group Department of Computer Science Swansea University R.S.Laramee@swansea.ac.uk

2. Robert S. Laramee r.s.laramee@swansea.ac.uk 2 http://cs.swan.ac.uk/~csbob/ 2 Overview Flow Visualization with a range of techniques:  Introduction to flow visualization  Flow data and applications  Streamline seeding  surfaces versus curves  Stream, path, and streak surfaces  Surface placement  Texture based flow visualization  Feature-based flow visualization  Conclusions and Acknowledgments

3. Robert S. Laramee r.s.laramee@swansea.ac.uk 3 http://cs.swan.ac.uk/~csbob/ 3 What is Flow Visualization?  A classic topic within scientific visualization  The depiction of vector quantities (as opposed to scalar quantities)  Applications include: aerodynamics, astronomy, automotive simulation, chemistry, computational fluid dynamics (CFD), engineering, medicine, meteorology, oceanography, physics, turbo-machinery design Challenges: to effectively visualize both magnitude + direction, often simultaneously large data sets time-dependent data What should be visualized? (data filtering/feature extraction)

4. Robert S. Laramee r.s.laramee@swansea.ac.uk 4 http://cs.swan.ac.uk/~csbob/ 4 What is Flow Visualization? Challenge: to effectively visualize both magnitude + direction often simultaneously magnitude only orientation only

5. Robert S. Laramee r.s.laramee@swansea.ac.uk 5 http://cs.swan.ac.uk/~csbob/ 5 1. direct: overview of vector field, minimal computation, e.g. glyphs, color mapping 2. texture-based: covers domain with a convolved texture, e.g., Spot Noise, LIC, ISA, IBFV(S) 3. geometric: a discrete object(s) whose geometry reflects flow characteristics, e.g. streamlines 4. feature-based: both automatic and interactive feature-based techniques, e.g. flow topology Flow Visualization Classification

6. Robert S. Laramee r.s.laramee@swansea.ac.uk 6 http://cs.swan.ac.uk/~csbob/ Swirl and Tumble Motion  swirl motion: characterized by motion about cylinder-aligned axis  more stable (easier)  tumble motion: characterized by motion about axis orthogonal to cylinder  unstable, more difficult

7. Robert S. Laramee r.s.laramee@swansea.ac.uk 7 http://cs.swan.ac.uk/~csbob/ 7 Characteristics of Integral Lines Advantages:  Implementation: various easy-to- implement streamline tracing algorithms (integration)  Intuitive: interpretation is not difficult  Applicability: generally applicable to all vector fields, also in three-dimensions Disadvantages:  Perception: too many lines can lead to clutter and visual complexity  Perception: depth is difficult to perceive, no well-defined normal vector  Seeding: optimal placement is very challenging (unsolved problem)

8. Robert S. Laramee r.s.laramee@swansea.ac.uk 8 http://cs.swan.ac.uk/~csbob/ 8 Automatic Streamline Seeding Videos

9. Robert S. Laramee r.s.laramee@swansea.ac.uk 9 http://cs.swan.ac.uk/~csbob/ Stream Surfaces Terminology:  Stream surface: a surface that is everywhere tangent to flow  Stream surface: the union of stream lines seeded at all points of a curve (the seed curve)  Next higher dimensional equivalent to a streamline  Unsteady flow can be visualized with a path surface or streak surface

10. Robert S. Laramee r.s.laramee@swansea.ac.uk 10 http://cs.swan.ac.uk/~csbob/ Stream Surfaces: Advantages  Separates (steady) flow: flow cannot cross surface (stream surfaces only)  Perception: Less visual clutter and complexity than many lines/curves  Perception: well-defined normal vectors make shading easy, improving depth perception  Rendering: surfaces provide more rendering options than lines: e.g., shading and texture- mapping etc. Disadvantages:  Construction/Implementation: more complicated algorithms are required to construct integral surfaces  Occlusion: multiple surfaces hide one another  Placement: placement of surfaces is challenging (video)

11. Robert S. Laramee r.s.laramee@swansea.ac.uk Constructing Streak Surfaces in 3D Unsteady Vector Fields (Video) Tony McLoughlin, Robert S. Laramee and Eugene Zhang

12. Robert S. Laramee r.s.laramee@swansea.ac.uk Stream Surface Placement (Video) Tony McLoughlin, Robert S. Laramee and Eugene Zhang

13. Robert S. Laramee r.s.laramee@swansea.ac.uk 13 http://cs.swan.ac.uk/~csbob/ Texture-Based Flow Visualization Texture-based flow visualization  Complete coverage  Flow features shown  Difficult to apply to 3D  Downstream direction shown tumble behavior non-ideal (video)

14. Robert S. Laramee r.s.laramee@swansea.ac.uk 14 http://cs.swan.ac.uk/~csbob/ Feature-Based Flow Visualization Feature-Based Visualization  Topological skeleton of flow is extracted explicitly  Features shown automatically  Applicable to 3D  Complete coverage  Downstream direction not shown swirl motion: very complex near top of chamber (video) red = saddle blue = sink green = source

15. Robert S. Laramee r.s.laramee@swansea.ac.uk 15 http://cs.swan.ac.uk/~csbob/ Acknowledgements Thank you for your attention! Any questions? We thank the following for their help:  Nick Croft, Matthew Edmunds,  Christoph Garth  Edward Grundy, Helwig Hauser  Rami Malki, Ian Masters,  Tony McLoughlin, Zhenmin Peng  Juergen Schneider, Benjamin Spencer  Xavier Tricoche, Daniel Weiskopf,  Eugene Zhang This work was partially funded by EPSRC EP/F002335/1